Low temperature centrifugal switch



July 28, 1964 J. G. RAY

LOW TEMPERATURE CENTRIFUGAL SWITCH Filed Aug. 31, 1951 INVENTOR JOHN G.RAY BY United States Patent 3,142,740 LOW TEMPERATURE CENTRIFUGAL SWITCHJohn Gilbert Ray, Mineola, N.Y., assignor, by mesue assignments, toSylvania Electric Products Inc., Wilmington, Del., a corporation ofDelaware Filed Aug. 31, 1951, Ser. No. 244,609 6 Claims. (Cl. 200-152)This invention relates to a mercury unshorter switch and moreparticularly to a low temperature centrifugal type of switch.

The prior art is well aware of various types of switches in whichmercury is used to make or break the contact. It is also aware of thecentrifugal type of switch in which the mercury is caused to passthrough a porous {plate before it can leave the chamber in which itfunctions as the electrical conducting medium between two leads. Theseswitches of the prior art are however limited in their use to certaintemperature conditions which are not always present where these switchesare to be used. This is particularly true in very cold climates. Therehas, therefore, been an apparent need for the development of a lowtemperature centrifugal type unshorter switch for some time.

An object of this invention is, therefore, to provide a mercury switchwhich is suitable for use at extremely low temperatures.

A further object of this invention is to provide a method for making aswitch which will function at extremely low temperatures and which willmeet the rigid specifications laid down for the normal centrifugal typeunshorter switches.

In accordance with this invention it has been found that these and otheradvantages incidental to its application can be obtained by replacingthe mercury in the switch with a mercury amalgam which has a freezingpoint lower than that of mercury.

In the drawings which illustrate an embodiment of the features of thisinvention FIGURE 1 is a front elevation partly in section of asub-assembly of the switch showing the cup-shaped member sealed to theporous filter disc.

FIGURE 2 is a front elevation of a switch showing the cup and filterdisc sealed to a member through which two electrical conducting leadsinsulated from one another project into the lower chamber and aresurrounded with mercury.

A specific embodiment of the centrifugal type of switch illustrated inthe drawings consists of a metallic eyelet 10 which is preferably madeof a material suitable for sealing to glass such as the iron nickel oriron nickel chr0- mium alloys which are frequently used in theelectronics industry for this purpose. The bottom end of this eyelet issealed off with a suitable glass 12 through which two spaced contactleads 14 pass. The top of the eyelet is sealed to a cup-shaped metallicelement 20 with a filter disc 18 sealed therebetween in a manner toseparate the entire unit into two separate chambers. The lower chamberas shown in FIGURE 2 at 16 contains mercury whereas the upper chamber isprovided with a number of glass balls 26 and a small pellet of thalliummetal.

Although it has been known for some time that a mercury thallium amalgamcontaining approximately 9% thallium has a freezing point of minus 590., this material could not be simply used to replace the mercury in themercury unshorter switches because of the fact that both thallium andthe mercury thallium amalgam. oxidize quite readily in the air and suchoxide film would result in the formation of a heavy scum which isdetrimental to the operation of an unshorter switch.

In accordance with this invention it has however been found that thisamalgam can be used for this purpose if it is found in the switch afterthe switch has been evacuated. In accordance with a preferred embodimentof this invention this can be accomplished in the following manner. Thesub-assembly as shown in FIGURE 1 is first made by taking a metallic cup20 and placing therein a measured amount of thallium '22 which haspreferably been cleansed in nitric acid and coated with a lacquer film24. Along therewith is introduced a quantity of glass beads or otherceramic pellet material whereupon a filter disc 18 is spot welded to thecup. A measured amount of mercury 16 is then placed into a unit whichhas been formed from a metallic eyelet 10 sealed at one end and with aglass head through which pass two spaced conductors 14. The sub-assemblyis then placed in position and the two units welded together. This ispreferably carried out in an evacuated atmosphere in order that anygases present in the unit may be exhausted prior to the actual sealingoperation. After the seal has been made the switch is placed in acentrifugal spinner where it is spun in such manner as to cause themercury to pass through the filter mechanism into the cup 20. Meanwhilethe heat given off during the welding operation will have caused thelacquer 24 to decompose and deposit carbonaceous material on the end ofthe cup. The mercury can thereby readily get in contact with thethallium and form an amalgam therewith. The switch is then preferablyvibrated so as to cause the glass balls to oscillate throughout theamalgam. Since the glass has a natural affinity for any scum which maybe present it removes it from the amalgam. Thereupon the switch is againplaced into a spinning mechanism which causes the amalgam to passthrough the filter disc into the lower chamber and provide a switchwhich is ready for use.

A switch of this type is well adapted for use at temperatures belowminus 40 C. where a small time delay is desired.

While the above description and drawings submitted herewith disclose apreferred and practical embodiment of the switch of this invention itwill be understood that the specific details of construction andarrangement of parts as shown and described are by way of illustrationand are not to be construed as limiting the scope of the invention.

What is claimed is:

1. A low temperature type switch having as its fluid type electricalconducting constituent a mercury thallium amalgam.

2. A low temperature mercury type switch having as its fluid typeelectrical conducting constituent a mercury thallium amalgam containingabout 9% thallium.

3. The method of making a low temperature centrifugal type switch havinga plurality of chambers separated by a porous disc comprising assemblingthe components with a thallium pellet in one chamber and mercury inanother, exhausting the air from the chambers, sealing the chambers fromthe atmosphere, spinning the switch to cause the mercury to flow throughthe porous disc and amalgamate with the thallium and spinning the switchwith the chambers reversed to cause the amalgam to seep through theporous disc and return to the first chamber.

4. The method of making a low temperature centrifugal type switch havinga plurality of chambers separated by a porous disc comprising assemblingthe components with allacquer coated thallium pellet in one chamber andmercury in another, exhausting the air from the chambers, sealing thechambers from the atmosphere and breaking down the lacquer coat on thethallium, spinning the switch to cause the mercury to flow through theporous disc and amalgamate with the thallium and spinning the switchwith the chambers reversed to cause the amalgam to seep through theporous disc and return to the first chamber.

5. The method of making a low temperature centrifugal type switch havinga plurality of chambers separated by a porous disc comprising assemblingthe components with a lacquer coated thallium pellet and glass beads inone chamber and mercury in another, exhausting the air from thechambers, sealing the chambers from the atmosphere and breaking down thelacquer coat on the thal l-iurn, spinning the switch to cause themercury to flow through the porous disc and amalgamate with thethallium, shaking the beads through the amalgam to remove any scum andspinning the switch with the chambers reversed to cause the amalgam toseep through the porous disc and return to the first chamber.

6. The method of making a low temperature centrifugal type switch havinga plurality of chambers separated by a porous disc comprising assemblingthe components with a lacquer coated nitric acid cleaned thallium pelletand glass beads in one chamber and mercury in another, exhausting theair from the chambers, sealing the chambers from the atmosphere andbreaking down the lacquer coat on the thallium, spinning the switch tocause the mercury to fiow through the porous disc and amalgamate withthe thallium, shaking the beads through the amalgam to remove any scumand spinning the switch with the chambers reversed to cause the amalgamto seep through the porous disc and return to the first chamber.

References Cited in the file of this patent UNITED STATES PATENTS2,145,468 Wangemann Jan. 31, 1939 2,284,899 Hedin June 2, 1942 2,387,313Wilson Oct. 23, 1945 2,508,018 Ellwood May 16, 1950

2. A LOW TEMPERATURE MERCURY TYPE SWITCH HAVING AS ITS FLUID TYPEELECTRICAL CONDUCTING CONSTITUENT A MERCURY THALLIUM AMALGAM CONTAININGABOUT 9% THALLIUM.